Vehicles may be powered by an engine and/or one or more batteries. For example, the engine may provide motive power for the vehicle and/or charge the batteries. The batteries, in turn, may provide power for starting the engine, and/or may provide motive power for the vehicle.
Both engines and batteries may produce a large quantity of waste heat, i.e., excess thermal energy, and close to half of the waste heat is typically dissipated into the atmosphere as an exhaust stream. Despite improvements in engine and combustion technology, nearly one-quarter of fuel energy may be expelled as waste heat in the exhaust stream. Therefore, significant gains in vehicle fuel economy may be realized if waste heat is converted into usable mechanical and/or electrical energy.